Reinforced monorail balloon catheter

ABSTRACT

The invention is a dilation catheter which comprises an elongated catheter shaft, a guide wire tube, and an angioplasty balloon. The distal end of the balloon is attached to the distal portion of the guide wire tube, and the proximal portion of the balloon is attached to the distal portion of the catheter shaft. A stiffening wire is attached to the inner wall of the catheter shaft at a plurality of points along its length. The distal extremity of the guide wire tube is decreased in size relative to the proximal portion of the guide wire tube. A fluid is contained within the guide wire lumen.

FIELD OF THE INVENTION

[0001] This invention relates to a dilatation catheter and moreparticularly to a dilatation catheter construction of particular utilityas a monorail dilatation catheter.

BACKGROUND OF THE INVENTION

[0002] Monorail dilatation catheters are becoming increasingly popularin angioplasty procedures because, unlike over-the-wire catheters thatrequire guide wire extenders to perform a catheter exchange, themonorail dilatation catheter construction enables one monoraildilatation catheter to be exchanged readily for another. U.S. Pat. No.4,762,129 to Bonzel discloses one such catheter having a guide wirelumen only at the distal segment of the catheter, for coupling thecatheter and the guide wire together. The guide wire tube extendsthrough the balloon, from the distal end of the catheter to a pointproximal to the balloon. Rapid exchange and manipulation of thedilatation catheter is facilitated because the catheter segment incontact with the surface of the guide wire is only as long as theballoon.

[0003] Although conventional monorail-type catheters allow rapidcatheter exchange, they tend to lack stiffness along their shaft lengthproximal to the exchange joint, at which point, the catheter gains thebenefit of the guide wire to impart stiffness to the catheter. This lackof stiffness along the proximal portion of the catheter makes itdifficult to advance the catheter through the body passageway. Bonzeladdresses this problem, in part, by providing an integral stabilizingmeans that extends from the catheter's proximal end, through theinflation lumen, to the distal end of the balloon.

[0004] The use of a stiffening wire (or mandrel) has also been proposedin a monorail catheter to provide controlled stiffness where neededwithout diminishing flexibility in the distal section of the catheter.Such stiffening wires, however, can buckle under compressive loads andpresent a potential risk of perforating the catheter wall.

[0005] The invention provides an improved monorail dilatation catheterwhich incorporates a stiffening wire wherein the likelihood of bucklingand/or perforation of the catheter shaft is substantially reduced if noteliminated.

[0006] Another feature of the invention is applicable to all ballooncatheters containing guide wire lumens, for example, both over-the-wireand rapid exchange (monorail) catheters. In such catheters, the guidewire lumen is normally flushed prior to use with a saline/heparinmixture to prevent blood coagulation in the lumen. The guide wire lumenmust be large enough to permit free movement of the catheter relative tothe guide wire. The larger the gap between the guide wire lumen and theguide wire, the freer the movement, but a smaller gap reduces thecatheter profile in the distal region of the catheter, thus facilitatingintroducing the catheter across the stenosis.

[0007] U.S. Pat. No. 5,209,728 to Kraus et al. addresses the problem ofhaving blood enter the catheter, and discloses a catheter provided witha tip member adapted to slidably receive a specially formed guide wire,so as to ensure a liquid-tight seal between the catheter and guide wire.The liquid-tight seal is formed by bringing the inner surface of thecatheter sufficiently close to the outer surface of the guide wire.Consequently, the inflation fluid is retained within the catheter, andblood is kept out of the catheter.

[0008] However, as is typically the case with over-the-wire catheters, areduced space between the catheter and the guide wire restricts theclear movement of the guide wire relative to the catheter. Suchresistance increases the tendency of the catheter to buckle when theoperator attempts to advance the catheter through the body passageway.It would, therefore, be desirable to provide a flexible dilatationcatheter having a stiffening wire adapted to impart stiffness to thecatheter to prevent buckling as it is manipulated through the bodypassageway. It would also be desirable to provide such a catheter thatlimits the amount of blood that enters the catheter, while at the sametime, facilitates the free movement of the guide wire with respect tothe catheter.

[0009] The invention further provides a balloon catheter which ismovable with respect to a guide wire, wherein the profile of the distalregion of the catheter is reduced without a sacrifice in freedom ofmovement of the catheter relative to the guide wire.

SUMMARY OF THE INVENTION

[0010] The present invention is directed towards a dilatation catheterwhich comprises an elongated catheter shaft, a guide wire tube and anangioplasty balloon. In conventional fashion, the distal end of theballoon is attached to the distal portion of the guide wire tube and theproximal portion of the balloon is attached to the distal portion of thecatheter shaft. The first aspect of the invention is directed towardspositioning a stiffening wire having a large diameter proximal portionand a small diameter distal portion, within the catheter shaft. Thestiffening wire is attached to the inner wall of the catheter shaft at aplurality of points along its length, thereby providing strength to theproximal portion of the catheter, without compromising the size of theinflation/deflation lumen.

[0011] The second feature of the invention is applicable to any catheterthat includes a guide wire lumen, such as an over-the-wire catheter or arapid exchange or monorail catheter. According to this feature of theinvention, a guide wire lumen is provided with a relatively large gapbetween the guide wire and the inner surface of the guide wire tube. Thedistal extremity of the guide wire tube is decreased in size for a shortdistance. The diameter of this decreased distal extremity approximatesthe diameter of the guide wire, thereby, substantially reducing theamount of blood that can enter the guide wire lumen. The large diameterportion of the guide wire lumen contains a saline/heparin mix which,because it is less viscous than blood, tends to flow into the gap withinthe small diameter lumen portion to reduce blood coagulation in thatportion and thereby reduce the risk of “seizing.” The relative movementbetween the balloon catheter and the wire creates a wiping action whichkeeps the wire clean.

[0012] The outer diameter of the distal extremity of the guide wire tubeis also reduced or tapered. As a result of this taper, the catheterprofile in the distal region of the catheter is reduced, facilitatingpassage of the catheter across a stenosis. As a result of the taperedguide wire tube, the profile of the distal portion of the balloon isappreciably decreased when the balloon is in its collapsed state. Thisfurther facilitates positioning the balloon across a stenosis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The foregoing and other features of the present invention will bemore readily apparent from the following detailed description anddrawings of a preferred embodiment of the invention in which:

[0014]FIG. 1 is a schematic plan view of a dilatation catheter inaccordance with the invention;

[0015]FIG. 2 is a detailed cross-sectional view of a catheter accordingto a preferred embodiment of the invention, illustrating the exchangejoint in detail;

[0016]FIG. 3 is a cross-sectional view along line 3-3 of FIG. 2;

[0017]FIG. 4 is a cross-sectional view along line 4-4 of FIG. 2, showingthe fused laminate in the exchange joint region;

[0018]FIG. 5 is a cross-sectional view along line 5-5 of FIG. 2;

[0019]FIG. 6 shows the balloon section of the catheter, illustrating theradiopaque coil spring;

[0020]FIG. 7 illustrates the tapered distal end of the catheter, showingthe reservoir formed inside the guide wire lumen;

[0021]FIG. 8 illustrates, in cross-section, a preferred method ofattaching the stiffening wire to the inner wall of the catheter shaft;

[0022]FIG. 9 illustrates, in cross-section, a second method forattaching the stiffening wire to the inner wall of the catheter shaft;and

[0023]FIG. 10 illustrates, in cross-section, another method forattaching the stiffening wire to the inner wall of the catheter shaft.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0024] A preferred embodiment of the invention as illustrated in FIGS. 1and 2 is a rapid exchange or monorail dilatation catheter comprising anelongated catheter shaft 20, a guide wire tube 22 (FIG. 2) and anangioplasty balloon 24.

[0025] In conventional fashion, the distal end of balloon 24 is attachedto the distal portion of the guide wire tube 22 and the proximal portionof the balloon is attached to the distal portion of the catheter shaft20. The balloon 24 is formed from suitable balloon material, forexample, polyethylene terephthalate (“PET”), nylon, or urethane. It ispreferred that the balloon 24 be coated with a highly lubricous,abrasion resistant coating. An example of this preferred coating is thatdisclosed in U.S. Pat. No. 5,077,352 to Elton, and assigned to theassignee of the present invention, C. R. Bard, of Murray Hill, N.J. TheElton '352 patent is incorporated by reference as if set forth in itsentirety herein.

[0026] As shown if FIG. 7, the wall thickness of the balloon 24 is notuniform. Considering only the distal sloping portion of the balloon 24,the wall of the balloon 24 is constructed such that the wall is verythin at the top of the sloping portion of the balloon, and becomesincreasingly thicker as one proceeds distally, down the sloping portionof the balloon to where the balloon 24 comes in contact with the guidewire tube 22. In a conventional catheter construction having a balloonattached to the catheter shaft, this thick-walled section of the ballooncontributes significantly to the increased balloon profile at theleading edge of the balloon.

[0027] According to the invention, however, the balloon 24 profile isreduced (1) by attaching the distal portion of the balloon 24 directlyto the guide wire tube 22, typically of a smaller outer diameter thanthe catheter shaft 20, and (2) by tapering the guide wire tube 22 in thedistal region. When the balloon 24 is in its collapsed state, thethickest segment of the wall of the balloon 24 corresponds to thetapered outer diameter segment of the guide wire tube 22, thus reducingthe balloon profile in the relevant distal portion of the balloon 24.

[0028] As shown in FIG. 6, a radiopaque coil spring 50 is positionedwithin the balloon 24 around the guide wire tube 22. A thin walledprotective sleeve 51 is placed over the coil spring. The radiopaque coilspring 50 enables the balloon 24 to be identified under X-rayfluoroscopy. The coil may be formed from, for example, 0.0025 inchspring coil material such as a gold-platinum combination, and isapproximately 4.5 millimeters long. The chosen coil parameters depend onthe desired flexibility characteristics to be imparted to the distal endof the catheter.

[0029] The balloon 24 is in fluid communication with the proximal end ofthe catheter via the annular space 64 between the catheter shaft 20 andthe stiffening wire 30 a which forms an inflation/deflation lumen (FIG.5). The inflation/deflation lumen 65 is maintained through the exchangejoint region 36 as explained below in the discussion of the exchangejoint region 36 (FIG. 4). Distal of the exchange joint region 36, theinflation/deflation lumen occupies the annular space between the guidewire tube 22, the catheter shaft 20, and the distal reduced diameterportion 30 b of the stiffening wire 30 (FIG. 3). Fluid, introducedthrough a connector at the luer fitting 28, causes the balloon 24 toexpand in conventional fashion.

[0030] The catheter shaft 20 extends distally from the luer fitting 28and terminates at the proximal end of the balloon 24 (FIG. 1). Thecatheter shaft 20 is skived at the point where a guide wire 60 isintroduced, forming a guide wire port 40. The portion of the cathetershaft 20 around the guide wire port 40, namely, the exchange jointregion 36, is subjected to increased stresses because the skivecompromises the integrity of the catheter shaft 20. For additionalstrength, an exchange joint sleeve 42 may be fused to the catheter shaft20 in the exchange joint region 36. The exchange joint sleeve 42 ispreferably made from the same material as the catheter shaft 20, forexample, polyethylene.

[0031] To further stiffen the catheter in the region of the exchangejoint 36, the guide wire tube 22 may be fused together with the cathetershaft 20 and the exchange joint sleeve 42, to form a fused polyethylenelaminate 46 (illustrated in cross-section in FIG. 4). In a preferredconstruction employing the fused laminate option, a flat mandrel (notshown) is temporarily positioned between the guide wire tube 22 and thecatheter shaft 20 to ensure that a fluid passageway (inflation/deflationlumen) is maintained through the fused laminate structure 46 after heatwelding. A patency mandrel (not shown) is also placed inside the guidewire tube 22. A removable shrink tubing is placed over the exchangejoint region 36 and a heat source is applied to the portion of theexchange joint region 36 where the fused laminate 46 is desired. Afterthe fused laminate 46 is formed, the shrink tubing is removed, and thepatency mandrel and the flat mandrel are withdrawn. As shown in FIG. 4,the distal reduced diameter portion 30 b of the stiffening wire 30 isembedded within the fused laminate 46.

[0032] In the preferred embodiment of the invention, the stiffening wire30, positioned within the catheter shaft 20, extends longitudinally fromthe luer fitting 28 to a point proximal to the balloon 24. As shown inthe proximal cut-away section of FIG. 1, the proximal end of thestiffening wire is bent to form a right-angled hook or flag. Plastic ismolded over this hook to form a button which snaps into a correspondingdetent within the luer fitting.

[0033] The precise point at which the stiffening wire 30 terminates isnot critical to the invention, and will depend on the desiredflexibility in the distal portion of the catheter.

[0034] According to the invention, the stiffening wire 30 is attached atspaced locations along its length to the inner wall 26 of the cathetershaft 20. The stiffening wire 30 is preferably attached by a pluralityof wire “tacks” 78 (FIG. 8). These wire tacks 78 are conveniently madefrom polyethylene, and are attached to the stiffening wire 30 before thestiffening wire 30 is inserted into the catheter. After the stiffeningwire 30 has been placed within the catheter shaft 20, the wire tacks 78are welded, glued, thermally adhered, or otherwise attached to the innerwall 26 of the catheter shaft 20. In a preferred construction, 3 twomillimeter long wire tacks 78 are spaced apart along the stiffening wire30. The first wire tack 78 is located approximately 40 centimetersproximal of the exchange joint 36. The second and third wire tacks 78are located approximately 63 and 86 centimeters proximal of the exchangejoint 36 respectively.

[0035] Numerous methods may be employed to periodically attach thestiffening wire 30 to the inner wall of the catheter shaft 20. Forexample, in another embodiment of the invention, sleeves 82 are used inplace of the wire tacks 78. The sleeves 82, wrapped around thestiffening wire 30, are adhered to the inner wall 26 of the cathetershaft 20 (FIG. 9). In yet another example, the stiffening wire 30 may beadhesively bonded to extruded material 86 and welded to the inner wall26 of the catheter shaft 20 (FIG. 10). Preferably, the wire tacks 78,the sleeves 82, and the extruded material 86 are made from the samematerial as the catheter shaft 20, for example, polyethylene.

[0036] By locking the stiffening wire 30 to the inner wall 26 of thecatheter shaft 20, the likelihood of the shaft buckling is reduced, andthe compressive force that can be applied to the proximal end of thecatheter is increased. Also, by using very small wire tacks 78 to attachthe stiffening wire 30 at periodic points along its length, the largestpossible inflation lumen 64 is maintained through the catheter shaft 20,thereby, decreasing inflation and deflation times.

[0037] As shown in FIG. 2, the stiffening wire 30 has a large diameterproximal portion 30 a and a smaller diameter or tapered distal portion30 b in the region of the exchange joint 36. The smaller diameterportion 30 b of the stiffening wire 30 imparts increased flexibility tothe distal segment of the catheter.

[0038] In a preferred embodiment, the stiffening wire 30 has a waveshaped distal end 30 c, so that the distal tip of the stiffening wire 30is deflected upwards, away from the wall of the catheter shaft 20. Eventhough the stiffening wire 30 is attached along its length, thestiffening wire 30 is capable of some longitudinally movement within thecatheter shaft 20. It is, therefore, conceivable that the distal tipwould be able to pierce the wall of the catheter shaft 20 as thecatheter is manipulated around a tight radius curve. The wave-likedistal end 30 c keeps the distal tip away from the wall of the cathetershaft 20.

[0039] The stiffening wire 30 is preferably made of MP35N alloy. TheMP35N alloy is an alloy of nickel, cobalt, molybdenum, and chromium. TheMP35N alloy is commercially available from Fort Wayne Metals of FortWayne, Ind.

[0040] When compared with stainless steel, the MP35N alloy has a higheryield strength, and imparts increased stiffness to the catheter shaft 20for a given diameter. Therefore, using MP35N alloy reduces theprobability that the catheter shaft 20 will buckle as the catheter isadvanced around a tight radius.

[0041] In a monorail catheter as shown, the guide wire tube 22 extendsfor only the distal portion of the catheter (for example, abouttwenty-five cm). The proximal end of the guide wire tube 22 forms theexchange joint 36 where the guide wire 60 can be introduced into theguide wire tube 22 (FIG. 2). The guide wire tube 22 is preferably madeof the same material as the catheter shaft 20, for example, a flexibleheat shrinkable material such as high density polyethylene.

[0042] As shown in FIG. 7, the guide wire tube 22 extends distally fromthe exchange joint 36 to the distal end of the catheter 20. According tothe present invention, the distal extremity 52 of the guide wire tube 22is decreased in size for a short distance. The inside diameter of thedistal extremity 52 approximates the diameter of the guide wire 60,thereby, substantially reducing the amount of blood that can enter theguide wire lumen. The reduced diameter distal extremity 52 is formed byfirst placing a mandrel within the guide wire tube 22, and then, pullingthe guide wire tube 22 through a heated die in order to reduce thediameter of the distal extremity 52 of the guide wire tube 22 toapproximate the size of the mandrel. The mandrel is then removed.

[0043] Although a monorail catheter is illustrated in FIG. 7, thisaspect of the invention is equally applicable to over-the-wiredilatation catheters and any other catheter containing a guide wiretube.

[0044] An anticoagulant is injected into the guide wire lumen 68 as thecatheter is being prepared, before the catheter is inserted into thepatient. The anticoagulant remains primarily in the large diameterportion of the guide wire lumen 68 (exaggerated in FIG. 7 for addedclarity). In a preferred monorail catheter construction, the proximalend of the guide wire tube is not sealed and a small quantity of theanticoagulant will escape from the proximal end. However, the adhesionof the anticoagulant to the inner surface of the guide wire tube 22 issufficient to maintain a satisfactory amount of anticoagulant within theguide wire lumen.

[0045] Because the anticoagulant is less viscous than blood, it tends tooccupy the gap within the small diameter lumen portion. As the guidewire 60 is moved relative to the catheter, the presence of theanticoagulant “wipes” the guide wire 60 clean. This wiping actionprevents any blood that may enter the guide wire lumen 68 from clottingalong the guide wire 60. The anticoagulant is preferably asaline/heparin mixture when the catheter is used in a blood vessel orartery, for example, a coronary artery.

[0046] A cross-link joint 74 is illustrated in FIG. 2 and may beemployed to connect the catheter shaft 20 to the guide wire tube 22,preferably in the region between the balloon 24 and the exchange joint36 (FIG. 2). The cross-link joint 74 efficiently couples the compressiveforce from the catheter shaft 20 to the distal tip 52 of the catheter.As the operator pushes on the catheter shaft 20, the cross-link joint 74transmits this force to the guide wire tube 22, thereby preventing anydeformation at the distal portion of the catheter.

[0047] The cross-link joint 74 may comprise an additional “block” ofpolyethylene that is fused, spot welded, or otherwise attached to boththe inner wall of the catheter shaft 20 and to the guide wire tube 22.The cross-link joint 74 may, for example, be positioned at a locationapproximately 5 millimeters from the distal tip of the stiffening wire30, and approximately 6 centimeters from the proximal end of the balloon24.

[0048] All dimensions given in this detailed description are forillustrative purposes only, and unless otherwise indicated, are notcritical to the present invention.

[0049] While the invention has been particularly shown and describedwith reference to a preferred embodiment thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A dilatation catheter comprising an elongatedcatheter shaft having an outer wall and an inner wall, the inner wallsurrounding a central lumen, a guide wire tube having an outer surfaceand an inner surface surrounding a guide wire lumen for receiving aguide wire extending through at least the distal portion of the cathetershaft, with a fluid channel between the outer surface of the guide wiretube and the inner wall of the catheter shaft, a balloon having a distalend and a proximal end, the proximal end being attached to the distalportion of the catheter shaft, and the distal end being attached to thedistal portion of the guide wire tube, the fluid channel serving as aninflation/deflation lumen for the balloon, wherein the guide wire lumenhas a distal portion of a first diameter and a proximal portion of asecond diameter larger than the first diameter, the length of the distalportion and the first diameter being selected such that when a guidewire is within the guide wire lumen, blood is substantially preventedfrom entering the proximal portion, but a less viscous anticoagulant inthe proximal portion can coat the surface of the guide wire within thedistal portion of the guide wire lumen.
 2. The dilatation catheter as inclaim 1 wherein the outer diameter of the distal portion of the guidewire tube is smaller than the outer diameter of the proximal portion ofthe guide wire tube.
 3. The dilatation catheter as in claim 1 whereinthe proximal portion of the guide wire lumen is adapted to receive ananticoagulant solution.
 4. The dilatation catheter as in claim 3 whereinthe anticoagulant solution is a heparin/saline mixture.
 5. Thedilatation catheter as in claim 1 further comprising a stiffening wirepositioned within the catheter shaft.
 6. The dilatation catheter as inclaim 5 wherein the stiffening wire is attached to the inner wall of thecatheter shaft at at least two spaced locations.
 7. The dilatationcatheter as in claim 6 wherein a plurality of wire tacks are used toattach the stiffening wire to the inner wall of the catheter shaft atthe spaced locations.
 8. The dilatation catheter as in claim 6 wherein aplurality of sleeves are used to attach the stiffening wire to the innerwall of the catheter shaft at the spaced locations.
 9. The dilatationcatheter as in claim 5 wherein the stiffening wire is made of MP35Nalloy.
 10. A monorail dilatation catheter comprising an elongatedcatheter shaft having an outer surface and an inner surface, the innersurface surrounding a central lumen, a guide wire tube having an outersurface and an inner surface, the inner surface surrounding a guide wirelumen for receiving a guide wire, the guide wire tube extending from anexchange joint in the shaft through the distal portion of the cathetershaft, with a fluid channel between the outer surface of the guide wiretube and the inner surface of the catheter shaft, a balloon connected atits distal end to the distal portion of the guide wire tube and at itsproximal end to the distal portion of the catheter shaft, the fluidchannel serving as an inflation/deflation lumen for the balloon, and astiffening wire positioned within the proximal shaft and attachedthereto at at least two spaced apart locations.
 11. The monoraildilatation catheter as described in claim 10 wherein the stiffening wirehas plastic attachment means associated therewith at the spaced apartlocations, the attachment means being thermally bonded to the shaft. 12.The monorail dilatation catheter as described in claim 11 wherein theplastic attachment means are wire tacks.
 13. The monorail dilatationcatheter as described in claim 11 wherein the plastic attachment meansare sleeves.
 14. The monorail dilatation catheter as described in claim11 wherein the stiffening wire is made of MP35N alloy.